Advanced Composition Explorer

Advanced Composition Explorer (ACE or Explorer 71) is a NASA Explorer program satellite and space exploration mission to study matter comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-time data from ACE are used by the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) to improve forecasts and warnings of solar storms.

Source: Wikipedia — Advanced Composition Explorer (CC BY-SA 4.0)